The present invention relates to precursor compounds useful for depositing alumina films used as a dielectric material in semiconductor devices, processes for preparing the compounds, and methods for vapor deposition of metallic films on silicon substrates using the compounds. More specifically, the present invention relates to compounds for forming alumina films upon adhesive layers or diffusion-preventive layers formed on substrates such as silicon substrates, processes for preparing the compounds, and methods for vapor deposition of metal oxide films.
According to the trend of large scale integration and miniaturization of semiconductor devices, the area occupied by memory cells, such as DRAM (xe2x80x9cdynamic random access memoryxe2x80x9d), is rapidly decreasing. Therefore, it is important in the area of DRAM capacitors to guarantee sufficient capacitance within a small area.
Capacitance increases in proportion to the dielectric constant of a dielectric material and the area of dielectric film used in capacitor and is in inverse proportion to the thickness of film, and therefore, three possible approaches may be considered in order to obtain sufficient capacitance with the limited cell area of DRAM.
First, the cell structure of the capacitor may be converted into a 3-dimensional one in order to maximize the effective area of dielectric film within the restricted small area. Actually in the 4 mega-DRAM, the capacitor having a plane structure has been replaced with that having a stack or trench structure, each of which is a 3-dimensional one, for the purpose of enlarging the effective area. Also in the 16 mega- or 64 mega-DRAM, the effective area has been secured using the more complicated 3-dimensional capacitor such as a fin cylinder or crown.
However, this approach has the problem that very complex capacitor structures need to be formed in a cell having a small area. Therefore, adoption of such 3-dimensional structures in the manufacture of more than 256 mega-DRAM, such as 1 giga-DRAM, is restricted due to their increasing complexity and high cost.
Second, the thickness of the dielectric film may be decreased to guarantee the capacitance. However, even though the 3-dimensional capacitor structure is used for maximizing the effective area, if the existing NO (Si3N4/SiOx) composite dielectric material is used, the thickness of dielectric film should be lowered to 40 to 45 xc3x85 in order for guaranteeing the minimum capacitance per cell, i.e. 25 to 30 fF (femptoFarad). Further, the reduction of thickness may result in the increase of current leakage due to the tunneling phenomenon or the increase of soft error by xcex1-particles, and consequently, the reliability of device may be threatened seriously.
Third, another dielectric material having a higher dielectric constant may be used instead of the currently used one for capacitors, such as for example, ONO structure such as SiO2/Si3N4/SiOx or NO structure such as Si3N4/SiOx, having a lower dielectric constant. Under the situation as explained above, extensive studies have been carried out for forming dielectric films of a capacitor using materials having higher dielectric constants than the earlier developed ones, whereby the capacitance can be stably secured in the manufacture of the next generation memory of more than 256 mega-DRAM. Use of such films having high dielectric constants may settle the problems such as difficulties in manufacturing processes, complexity of capacitor structures, reduction of reliability of devices, etc. One of the dielectric films currently studied for that purpose is alumina film.
Since 1970s, the study of alumina CVD using commercially available alkyl aluminum and aluminum alkoxide was performed in the USA and Japan. The typical aluminum compounds used have been trimethylaluminum having the formula Al(CH3)3 and aluminum isopropoxide having the formula Al(O-iC3H7)3.
The compounds as recommended above, however, show some problems when they are used as precursors. The alkylaluminum compound, trimethylaluminum, has been used for various purposes in different technical areas, and thus, it can be commercially purchased from the market with a low cost. Also, it has the advantage of being effectively used as the CVD precursor because it exists as a liquid having a high vapor pressure at room temperature. However, since the vapor deposition of film is achieved at a high temperature of 300 to 400xc2x0 C., the undesirable impurity carbon may remain in the alumina film and a very careful handling may be required due to the explosive inflammation caused by the trifling contact of alkylaluminum compound with the ambient air, which commonly occurs when the alkyl aluminum compound is used.
The aluminum alkoxide compound, i.e., aluminum isopropoxide, is cheap and commercially available. Also, it does not inflame upon contact with moisture. However, it has the disadvantage that since it exists as a solid at room temperature or its vapor pressure is low, high temperature heating may be required at the stage of vapor deposition which results in the decomposition of the compound, or the deposition process may not be reproducible due to the condensation of the compound.
In the case of vapor-deposition of aluminum films using such compounds, several problems may occur, such as for example, the introduction of undesirable carbon impurities into the aluminum film; the difficult to achieve process reproducibility which is caused by the decomposition of precursor compound in the reactor due to the high temperature heating; and explosive inflammation caused by the reaction of the compound with moisture, etc.
In order to solve the problems mentioned above, the present inventor has complemented the earlier invention relating to a precursor compound for forming aluminum film via chemical vapor deposition method and process for preparing the same, which was filed by the present inventor as Korean Patent App. No. 98-38572, and as a result, completed the present invention.
The present invention provides a novel aluminum compound and process for preparing the same, by which can be solved some problems found in the prior art for precursor compounds for alumina and aluminum CVD, such as for example, difficult to achieve reproducibility of film deposition processes, explosive inflammation of the compounds upon contact with moisture, and the residual impurities in the film. Further, according to the present invention, the skilled person may enjoy the large range of selection of the precursor compounds.
In one aspect, the present invention provides an organometallic complex useful for depositing a highly pure alumina film on a substrate by chemical vapor deposition, having the Formula I:
Rxe2x80x2Rxe2x80x3Rxe2x80x2xe2x80x3Al:Lnxe2x80x83xe2x80x83(I)
wherein Rxe2x80x2, Rxe2x80x3 and Rxe2x80x2xe2x80x3 are independently selected from alkyl, perfluoroalkyl or alkoxy each of which has 1 to 5 carbon atoms, or borate (BH4); L is one or more organic Lewis bases capable of providing an unshared electron pair to the aluminum metal center selected from thiophene, thiopyran and organic amines of the Formulae II or III: 
wherein R is an alkyl having 1 to 4 carbon atoms; R1, R2, R21, R22, R23 and R24 are independently selected from hydrogen (H) or alkyl having 1 to 2 carbon atoms; X is oxygen (O) or nitrogen having alkyl group; k and l are integers of 1 to 3; m is an integer of 2 to 8; and n is an integer of 1 or 2.
In a second aspect, the present invention provides a vapor deposition precursor composition comprising an organometallic compound as described above and one or more heterocyclic amine solvents.
In a third aspect, the present invention provides a process for alumina film formation including the step of vapor depositing an alumina film on a substrate, wherein the source of aluminum in the alumina film is a vapor deposition precursor including an organometallic compound of the Formula:
Rxe2x80x2Rxe2x80x3Rxe2x80x2xe2x80x3Al:Lnxe2x80x83xe2x80x83(I)
wherein Rxe2x80x2, Rxe2x80x3 and Rxe2x80x2xe2x80x3 are independently selected from alkyl, perfluoroalkyl or alkoxy each of which has 1 to 5 carbon atoms, or borate (BH4); L is one or more organic Lewis bases capable of providing an unshared electron pair to the aluminum metal center selected from thiophene, thiopyran and organic amines of the Formulae II or III: 
wherein R is an alkyl having 1 to 4 carbon atoms; R1, R2, R21, R22, R23 and R24 are independently selected from hydrogen (H) or alkyl having 1 to 2 carbon atoms; X is oxygen (O) or nitrogen having alkyl group; k and l are integers of 1 to 3; m is an integer of 2 to 8; and n is an integer of 1 or 2.
In a fourth aspect, the present invention provides a process for preparing an organometallic compound of the Formula:
Rxe2x80x2Rxe2x80x3Rxe2x80x2xe2x80x3Al:Lnxe2x80x83xe2x80x83(I)
wherein Rxe2x80x2, Rxe2x80x3 and Rxe2x80x2xe2x80x3 are independently selected from alkyl, perfluoroalkyl or alkoxy each of which has 1 to 5 carbon atoms, or borate (BH4); L is one or more organic Lewis bases capable of providing an unshared electron pair to the aluminum metal center selected from thiophene, thiopyran and organic amines of the Formulae II or III: 
wherein R is an alkyl having 1 to 4 carbon atoms; R1, R2, R21, R22, R23 and R24 are independently selected from hydrogen (H) or alkyl having 1 to 2 carbon atoms; X is oxygen (O) or nitrogen having alkyl group; k and l are integers of 1 to 3; m is an integer of 2 to 8; and n is an integer of 1 or 2; including the step of combining in the absence of a solvent the organic Lewis base and a tri-substituted aluminum compound of the formula Rxe2x80x2Rxe2x80x3Rxe2x80x2xe2x80x3Al, wherein Rxe2x80x2, Rxe2x80x3 and Rxe2x80x2xe2x80x3 are as defined above.